Agricultural harvesting heads such as draper platforms are designed to follow closely along the ground as they harvest crops. To ensure that they follow the ground closely, they are configured to contact the ground and apply a slight ground force to the ground or, alternatively, to travel slightly over the surface of the ground without making contact.
Hydraulic and electric circuits are typically provided to ensure that only a small portion of their weight is actually pressed against the ground. As the ground rises and falls underneath the agricultural harvesting head, the position of the agricultural harvesting head is adjusted up and down with respect to the agricultural combine on which the agricultural harvesting head is supported. This permits the agricultural harvesting head to adjust to changing terrain.
In recent years, articulated agricultural harvesting heads have been designed. Articulated heads comprise two or more elongated sections that are hinged to each other. As the terrain changes, each section is designed to rise and fall with respect to the ground independently of the other sections. In a three-section articulated agricultural harvesting head, for example, the two end sections are hingeably connected to a center section. The center section is supported on the agricultural combine itself. The two outer hinged sections are supported on the ground, and also are supported on the center section itself.
In CA 2,665,589 A1, the outer hinged sections of the agricultural harvesting head are supported on wheels. As the terrain changes, the terrain pushes against the wheels, which in turn raises and lowers the outer hinged sections with respect to the center section.
In US 2003/0074876 A1, an arrangement of linkages, levers, and springs are used to couple the outer sections of the agricultural harvesting head to the central section.
The Geringhoff company has a draper called “Triflex” that uses an accumulator (a hydraulic spring) to control the downforce applied to the ground.
One problem with all of these arrangements is their inability to respond quickly to rapid changes in terrain. As the terrain changes, it rises up and occasionally hits the bottom of the agricultural harvesting head. When this happens, the ground exerts not only an upward force but rearward forces as well. Furthermore, changes in crop thickness can also increase the rearward force acting upon the agricultural harvesting head. When these rearward forces act upon the sides of the agricultural harvesting head, particularly when it is a wide harvesting head, they can be so substantial that they damage the harvesting head or the combine that supports it. This can occur, for example, by pushing one side or the other of the harvesting head rearward, and bending the feederhouse, which is typically not designed to be twisted to one side or the other.
As the crop gets thicker and harder to cut, the operator typically increases the commanded operating height of the agricultural harvesting head. In this context, the “commanded operating height” is the set point or reference height to which the automatic header height control (AHHC) circuit tries to maintain the agricultural harvesting head above the ground. In this manner, the operator reduces the rearward load acting upon the harvesting head and thus, the risk of damage to the agricultural harvesting head due to sudden increases in rearward load. As the terrain under the agricultural harvesting head fluctuates, the automatic header height control circuitry will try to maintain this commanded operating height of the head above the ground.
Conversely, as the crop to be cut gets lighter (i.e. thinner) and easier to cut, the operator typically decreases the commanded operating height of the agricultural harvesting head, thereby permitting the agricultural harvesting head to cut closer to the ground. Since lighter crop growth exerts smaller rearward forces on the agricultural harvesting head, the agricultural harvesting head can be operated closer to the ground, thereby harvesting more crop closer to the ground.
It is not possible for the operator to continually adjust the commanded operating height of the agricultural harvesting head. It is too time consuming.
What is needed, therefore, is an improved arrangement for supporting an agricultural harvesting head that reduces the risk of damage due to excessive contact with the ground and dense crop that acts in a rearward direction.
It is an object of this invention to provide such an arrangement.